Jellyfish

Noun

1. An almost transparent aquatic animal; any one of the acalephs, especially one of the larger species, having a jellylike appearance.
2. Any of various species of cnidarians in the subphylum Medusozoa, including box jellyfish (class Cubozoa), true jellyfish (class Scyphozoa), stalked jellyfish (class Staurozoa), and certain hydrozoans. The medusa phase of these animals rather than a younger life stage.
3. The medusa phase of these animals rather than a younger life stage.
4. A ctenophore, a member of the phylum Ctenophora (comb jellies).
5. A sudoku technique involving possible cell locations for a digit, or pair, or triple, in uniquely four rows and four columns only. This allows for the elimination of candidates around the grid.